1. Field of the Invention
The present invention relates to a process for treating architectural materials to give them new functionality.
2. Description of the Background
The materials more particularly targeted are those in buildings as fascia, cladding, roofing or flooring material and are capable of offering a certain level of porosity/permeability with respect to relatively liquid fluids, such as water, to a detectable depth, for example of at least a few microns. These are, in particular, materials such as fascia coatings, concrete slabs and paving stones, architectonic concrete, tiles, slates and all materials of various forms based on cement composition, concrete or terracotta, or stones such as granite or marble.
The new functionality which the invention is seeking to give them concerns anti-soiling, antifungal and/or bactericidal properties, obtained using semiconductor materials based on a metal oxide or sulphide, in particular based on titanium oxide crystallized in anatase form, having photocatalytic activity: specifically, these materials are capable, in a known manner, of initiating radical-mediated reactions bringing about the oxidation and degradation of organic products under the effect of a radiation of adequate wavelength, this being ultraviolet radiation as regards titanium oxide.
There is currently a genuine demand for this novel type of functionality: specifically, these materials used in construction have a tendency very quickly to lose their new appearance on account, firstly, of their presence in soiling environments, and, secondly, of their porosity and/or surface roughness, which facilitate the attachment of the soiling. The soiling frequently encountered is, for example, micro-organisms which affect not only the appearance, but also, in the long term, the structural properties of the material. Thus, tiles become covered in algae, lichen or moss in a humid environment. This is likewise the case for concrete slabs and paving stones when they are used to make patios or in the enhancement of gardens, and fascia coverings also constitute a suitable substrate for the growth of vegetation of this type.
Soiling also arises from the encrustation generated by urban organic pollution, consisting in particular of industrial or motor vehicle soot, this soot additionally having a tendency to facilitate the attachment of mineral dust to the material, creating dark crusts on its surface.
Mention may also be made of soiling affecting flooring slabs, such as spent motor oil and grease, and fascias, such as graffiti.
Giving all these materials a “self-cleaning” function by means of photocatalytic active components thus appears to provide an at least partial response to this problem, by at the very least making it possible to spread out the cleaning operations, these active components promoting the degradation of organic species in the presence of oxygen, water and an appropriate radiation such as UV, i.e. generally under conditions of exposure to the natural ambient atmosphere.
Certain publications already mention the use of photocatalytic titanium oxide particles for treating architectural materials in order to obtain an anti-soiling effect.
Thus, patent application WO 97/10185 describes the deposition of photocatalytic coatings onto glass substrates, these coatings comprising photocatalytic TiO2 particles and a mineral binder obtained from the high-temperature thermal decomposition of organo-metallic precursors.
Mention may also be made of patent application WO 98/05601 which describes the incorporation of photocatalytic TiO2 particles directly into a hydraulic binder for cement compositions to make fascia coverings, and patent application EP-0 633 064 A1 describing coatings combining photocatalytic TiO2 particles and an adhesive which has little capacity for photocatalytic degradation, such as a fluoropolymer, for treating glass or metal substrates in particular.